This application claims the priority of Federal Republic of Germany patent application no. 101 23 491.0, filed May 15, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an adjustable suspension strut for a motor vehicle and a method of adjusting a suspension strut.
DE 195 29 580 C2 describes an adjustable suspension strut that has a damping element. The damping element is enveloped by a helical spring and has a damping cylinder and a piston rod, which can be moved in and out in the damping cylinder. One end of the helical spring is braced on a first spring seat. Spaced apart from the first spring seat, a second spring seat is fastened to the piston rod. Thus, the second spring seat automatically follows the in and out movements of the piston rod. A first ring cylinder can be slid axially with a first guide surface on the damping cylinder. A second ring cylinder is arranged stationarily between the first ring cylinder and the damping cylinder. The first ring cylinder is guided with a second guide surface on a third guide surface of the second and/or internal ring cylinder. To adjust in the axial direction of the first ring cylinder there is a working chamber, whose volume can be changed and which is defined by at least the first and the second ring cylinder, whereby the different axial positions of the first ring cylinder are set by filling or emptying the working chamber. As a function of the fill quantity of a working medium in the working chamber, the first ring cylinder assumes an axial position on the damping cylinder. Since the first spring seat is fastened to the first ring cylinder, the overall length of the suspension strut can be varied.
Such adjustable suspension struts are usually used for level adjustment, that is to change the ground clearance of the vehicle. Another field of application is the position adjustment of a vehicle in order to achieve optimal handling performance even under varying road and driving conditions. To actuate the suspension struts of a vehicle, there is at least one valve unit, which connects the working chambers of the suspension struts to a tank or a pressure medium conveyor, for example a pump. To control the valve unit, there is a controller. The actuation of adjustable suspension struts is described, for example, in DE 42 31 641 A1.
One drawback with the suspension strut described above is that the control of the position and/or level adjustment is very expensive to operate.
Therefore, the object of the invention is to provide an adjustable suspension strut that enables a simplification of the control tasks.
This problem is solved with an adjustable suspension strut for a motor vehicle, which suspension strut is described hereinafter.
One of the advantages of the present invention is that the displaceability in the axial direction of both the first and the second ring cylinder enables a movement of one of the two ring cylinders in relation to the other ring cylinder, in particular for a hydraulically actuated position and/or level adjustment. In addition, both ring cylinders can be slid together in the axial direction on the damping element through manual adjustment of the adjusting element, thus achieving a manual change in the length of the suspension strut. In other words, the length of the suspension strut can be manually adjusted, and proceeding from this basic manual adjustment, the level and/or position can then be adjusted hydraulically. When the length of the suspension struts of a vehicle is set manually by a basic adjustment, the result for the vehicle is a defined and/or balanced starting position, so that the actuation for the position and/or level adjustment is easier to carry out than in the prior art.
A preferred embodiment is a simpler assembly of the suspension strut. In this embodiment it is also advantageous for the essentially conventional damping elements to be equipped with the two ring cylinders so that no fundamentally new construction of damping elements is necessary. Moreover, a modular construction, wherein the two ring cylinders can be retrofitted, as a prefabricated unit, on a damping element, is conceivable.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.